Intensive therapy is currently accepted as the standard of care to reduce the risk of long term complication in patients with diabetes of all ages. However, intensive therapy is frequently complicated by hypoglycemia. In comparison to adults, young children and adolescents have even more lifestyle characteristics that make them prone to hypoglycemia, which then becomes a dangerous complication and a major limiting factor of intensive treatment and good diabetes control. With current home glucose monitoring capabilities it is difficult to accurately define the true incidence, duration, and severity of hypoglycemia in children with diabetes. A continuous glucose monitoring system (CGMS) has recently become available as a tool to more closely examine blood glucose patterns, by recording up to 288 glucose measurements a day (864 glucose readings over a 72 hour period). The purpose of the proposed study is to elucidate the extent of hypoglycemia and the factors that contribute to hypoglycemia in children with and without diabetes. In this descriptive study, four age groups of children will be studied: defined by children 2-6, 6-10, 10-14, and 14-18 years of age. Grouping by age will assure an appropriate sample of children of different ages, as well as a large prepubertal cohort. Eighteen children with diabetes will be included in each age group for a total of 72 patients with diabetes. Nine children without diabetes will serve as controls for each age group in order to study the normal physiologic glucose variability. During the four years of data collection, subjects will participate for one to three years, depending on the time of enrollment. They will be fitted with the CGMS for three days, quarterly, alternating week, and weekend intervals. Data will be obtained on the child?s medical history, blood glucose levels, genotyping, and dietary intake. Activity will be monitored by accelerometry. Cognitive functioning, school performance, behavior, and adjustment to diabetes will be measured as potential factors contributing to the risk of hypoglycemia. In summary, CGMS in children with diabetes will provide valuable information on hypoglycemia frequency and severity, and the risk factors associated with this serious complication of intensive diabetes management in children.